This invention relates to an optically clear thermoplastic resin composition, a method to synthesize the composition and articles made from the compositions.
Polycarbonate is a useful engineering plastic for parts requiring clarity, high toughness, and, in some cases, good heat resistance. However, polycarbonate also has some important deficiencies, among them poor chemical and stress crack resistance, poor resistance to sterilization by gamma radiation, and poor processability. Blends of polyesters with polycarbonates provide thermoplastic compositions having improved properties over those based upon either of the single resins alone. Moreover, such blends are often more cost effective than polycarbonate alone. The miscibility of PC with the polyesters gives the blends the clarity needed, but this is restricted to (semi) aliphatic polyesters such as poly (cyclohexane dimethanol cyclohexane dicarboxylate) (PCCD) or a glycolized copolyester such as polyethylene glycol cyclohexane dimethanol terephthalate (PCTG).
U.S. Pat. Nos. 4,188,314, 4,125,572; 4,391,954; 4,786,692; 4,897,453, and 5,478,896 relate to blends of an aromatic polycarbonate and poly cyclohexane dimethanol phthalate. U.S. Pat. No. 4,125,572 relates to a blend of polycarbonate, polybutylene terephthalate (PBT) and an aliphatic/cycloaliphatic iso/terephthalate resin. U.S. Pat. No. 6,281,299 discloses a process for manufacturing transparent polyester/polycarbonate compositions, wherein the polyester is fed into the reactor after bisphenol A is polymerized to a polycarbonate. WO2004076541 describes thermoplastic composition based of a polycarbonate polymer with embedded polysiloxane domains having an average domain size between 20 and 45 nanometers or between 20 and 40 nanometers, which are translucent in nature.
Condensation copolymers having polysiloxane and polycarbonate blocks are known. Representative of such polymers are those disclosed by U.S. Pat. Nos. 4,681,922, 3,189,662, 3,419,635, and 3,832,419 have an elastomeric character and useful as adhesives, coatings, sealants, roofing material, impact modifying additives and the like. While U.S. Pat. No. 4,794,141 discloses molding compositions containing polydiorganosiloxane/polycarbonate block copolymers, elastomeric polymers. The elastomeric polymer is described as a hydrogenated block copolymer of a vinyl aromatic monomer and a conjugated diene.
A polymer blend comprising a polyalkylene terephthalate, an organopolysiloxane-polycarbonate block copolymer, and a halogenated copolycarbonate having improved impact, heat distortion and flame retardant properties is described in U.S. Pat. No. 4,155,898. U.S. Pat. Nos. 4,161,498; 4,155,898; and 4,161,469 describe polyalkylene terephthalate resin and all organopolysiloxane-poly-carbonate block copolymer having impact and heat distortion properties. U.S. Pat. No. 4,994,532 describes functionalized polydimethylsiloxane fluids which react with polycarbonate in the melt to form polydimethylsiloxane/polycarbonate block copolymers. The resultant copolymers are described as transparent and show improved flow. The U.S. Pat. No. 5,026,791 relates to an aromatic carbonate polymer having a siloxane Unit in the backbone of the polymer. U.S. patent application Ser. No. 10/882,529 disclose a transparent/translucent composition comprising 1 to 30 weight percent of a cycloaliphatic polyester and greater than or equal to 40 weight percent of a polyorganosiloxane/polycarbonate block copolymer, while U.S. patent application Ser. No. 10/373,547 teaches the compositions with polyesters with impact modifiers. However in the above compositions low temperature ductility is sacrificed for better flow and impact, and use of impact modifiers leads to a decrease in the transparency. The polymers of polycarbonate with the siloxane, while useful, have lower than desired flow properties, require high torque or high molding pressures during processing. The siloxane-carbonate polymers are also known to possess inadequate impact strength at low temperatures and inadequate resistance to distortion.
From the standpoint of ease of processing, it is desirable for a thermoplastic to have higher melt flow properties. There is a continuing need for polycarbonate polyester blends having a good balance of optical property, processability, solvent resistance and good mechanical and thermal properties.